1. Field of the Invention
The present invention relates to an image-recording material usable for planographic printing plate precursors, color proofs, photoresists and color filters, and to novel cyanine dyes favorable for it. In particular, the invention relates to a negative image-recording material for heat-mode exposure systems, which is usable for a planographic printing plate precursor on which an IR laser is scanned on the basis of the digital signals from a computer or the like to directly make a planographic printing plate; and relates to novel cyanine dyes of high IR absorbing property.
2. Description of the Related Art
For a system of directly making printing plates from digital data of a computer, heretofore proposed have been  less than 1 greater than  electrophotography,  less than 2 greater than  exposure of photopolymerizable materials to blue or green-emitting lasers,  less than 3 greater than  silver salts lamination on photosensitive resin, and  less than 4 greater than  silver diffusion transfer photography.
However, these all have some drawbacks. Specifically, the image-forming process of electrophotography  less than 1 greater than  is troublesome, in requiring complicated steps of electric charging, exposure to light and development, and this requires a complicated, large apparatus. Photopolymerizable plates for  less than 2 greater than  are highly sensitive to blue and green light, and are difficult to handle in light rooms. In the processes of  less than 3 greater than  and  less than 4 greater than  using silver salts, development is troublesome, and, in addition, the wastes contain silver.
On the other hand, the recent development of laser technology has been remarkable, and high-power, small solid lasers and semiconductor lasers for emitting IR radiation within a wavelength range of from 760 nm to 1200 nm are easily available. For a light source for directly making a printing plate from digital data of a computer or the like, these lasers are extremely useful. However, many practicable photosensitive recording materials are sensitive to visible light falling within a wavelength range of at most 760 nm, to which, therefore, these IR lasers are not applicable for recording images thereon. Accordingly, recording materials capable of being processed with IR lasers are desired.
An image-recording material capable of being processed with an IR laser is described in U.S. Pat. No. 4,708,925, which includes an onium salt, a phenolic resin and a spectral sensitizer. This is a positive image-recording material, in which the onium salt and the phenolic resin express dissolution resistance to developers, and is not a negative image-recording material as in the present invention. On the other hand, a negative image-recording material is disclosed in U.S. Pat. No. 5,340,699, which includes an IR absorber, an acid generator, a resol resin and a novolak resin. For image formation thereon, however, this material requires heat treatment after exposure to a laser. Therefore, a negative image-recording material not requiring heat treatment after exposure to light has been desired.
For example, Japanese Patent Application Publication (JP-B) No. 7-103171 discloses a recording material that includes a cyanine dye having a specific structure, an iodonium salt, and an ethylenically unsaturated double bond-having addition-polymerizable compound. This does not require heat treatment after imagewise exposure to light. However, the strength of the image area of this material is low. Therefore, this is unfavorable for planographic printing plates, as the number of prints from a planographic printing plate is small.
The object of the invention is to provide a negative image-recording material which can be imagewise exposed to IR rays from an IR-emitting solid laser or semiconductor laser to directly make a printing plate from the digital data of a computer or the like, and which, when the obtained printing plate is used as a planographic printing plate, ensures well cured image formation on the printing plates even though not heated for image formation thereon, and therefore exhibits good printing durability to ensure a large number of good prints from the printing plates; and to provide novel cyanine dyes favorable for IR absorbents for the image-recording material of the type having the excellent characteristics as above.
Having specifically noted the constituent components of negative image-recording materials and having assiduously studied them, the present inventors have found that, when a cyanine dye having a specific partial structure is used for the IR absorbent in a negative image-recording material, then the above-mentioned object can be attained. On the basis of this finding, the present inventors have completed the invention.
Specifically, the invention provides a negative image-recording material for heat-mode exposure systems, which comprises (A) an IR absorbent including cyanine dye having an electron-withdrawing group or a heavy atom-containing substituent in at least one terminal aromatic ring, (B) a radical generator such as onium salts and (C) a radically-polymerizable compound, wherein images are formed therein by imagewise exposure to IR rays.
The invention also provides a negative image-recording material for heat-mode exposure systems, which comprises (Axe2x80x2) an IR absorbent of the following general formula (1), (B) a radical generator and (C) a radically-polymerizable compound.
A+xe2x88x92Q=B Xxe2x88x92xe2x80x83xe2x80x83(1) 
wherein 
In formula (1), A+ and B are terminal groups represented by the formulae mentioned above; and R1 and R2 each independently represent an optionally-substituted hydrocarbon group having at most 20 carbon atoms. Ar1 and Ar2 may be the same or different, each representing an optionally-substituted aromatic hydrocarbon group or heterocyclic group. Y1 and Y2 may be the same or different, each representing a sulfur atom, an oxygen atom, a selenium atom, a dialkylmethylene group having at most 12 carbon atoms, or xe2x80x94CHxe2x95x90CHxe2x80x94. Z1 and Z2 may be the same or different, each representing a substituent selected from a hydrocarbon group, an oxy group, an electron-withdrawing substituent and a heavy atom-containing substituent, and at least one of Z1 and Z2 is an electron-withdrawing group or a heavy atom-containing substituent. n and m each independently indicate 0 or a positive integer, and the sum of n and m is at least 1.
Q represents a pentamethine group or a heptamethine group, optionally substituted by substituent(s) selected from an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a dialkylamino group, a diarylamino group, a halogen atom, an alkyl group, an aralkyl group, a cycloalkyl group, an aryl group, an oxy group and a substituent of the following general formula (2); and Q may have a cyclohexene, cyclopentene or cyclobutene ring containing continuous three methine chains. 
wherein R3 and R4 each independently represent a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, or an aryl group having from 6 to 10 carbon atoms; and Y3 represents an oxygen atom or a sulfur atom. Xxe2x88x92 represents a counter anion optionally existing for charge neutralization of the compound of formula (1).
Preferably, the cyanine dyes of formula (1) have halogen atoms or carbonyl substituents in the two terminal aromatic rings.
In addition, the present invention provides a negative image-recording material f or heat-mode exposure systems, which comprises (Axe2x80x3) an IR absorbent of the following general formula (3), (B) a radical generator and (C) a radically-polymerizable compound, wherein images are formed therein by imagewise exposure to IR rays: 
wherein R5 and R6 each independently represent a linear or branched alkyl group having at most 20 carbon atoms, optionally substituted with any of an aryl group, an alkenyl group, an alkoxy group, a hydroxyl group, a sulfo group, a carboxyl group and an acyloxy group;
Ar3 and Ar4 each independently represent a hydrogen atom, an alkyl group having from 1 to 4 carbon atoms, or an aryl group having from 6 to 10 carbon atoms, the alkyl group and the aryl group for these may be optionally substituted with any of an alkyl group, an aryl group and a halogen atom, and Ar3 and Ar4 may be bonded to each other;
Y4 and Y5 maybe the same or different, each representing a sulfur atom, an oxygen atom, a selenium atom, a dialkylmethylene group having at most 12 carbon atoms, or xe2x80x94CHxe2x95x90CHxe2x80x94;
Z3 to Z10 may be the same or different, each representing a hydrogen atom, a hydrocarbon group, an oxy group, an electron-withdrawing group or a heavy atom-containing substituent, and at least one of these is an electron-withdrawing group or a heavy atom-containing substituent, and two neighboring groups of Z3 to Z10 may be bonded to each other to form a 5- or 6-membered ring;
Xxe2x88x92 represents a counter anion optionally existing for charge neutralization of the compound of formula (1).
Though not clear, the advantages of the negative image-recording material of the invention may result from the action of the cyanine dye therein, which has an electron-withdrawing substituent in at least one terminal aromatic ring in the molecule and which serves as an IR absorbent in the material. Specifically, in the material, the cyanine dye will promote the polymerization of the radically-polymerizable compound to form a firm recording layer, thereby improving the printing durability of the processed material. Concretely, in addition to the decomposition of the ordinary initiator through photo-thermal conversion in the material, the ionization potential of the electron-withdrawing group-substituted cyanine dye therein may be increased, and the cyanine dye excited through exposure to IR rays will readily interact with the initiator to thereby increase the probability of radical generation, and, as a result, the polymerization of the radically-polymerizable compound may be there by promoted. The IR absorbent, cyanine dye having a heavy atom-containing substituent in at least one terminal aromatic ring may also promote the polymerization of the radically-polymerizable compound to thereby enhance the printing durability of the processed material. For this, it is presumed that the IR absorbent will easily undergo triplet excitation when exposed to IR rays, and the thus triplet-excited IR absorbent may inactivate dissolved oxygen acting as a polymerization inhibitor and may promote the decomposition of the radical generator through some interaction with it.
We, the present inventors have further found that novel cyanine compounds having a specific structure are especially useful for the IR absorbent in the recording material of the invention.
Accordingly, the invention also provides a cyanine dye of the following general formula (3-1): 
wherein R5 and R6 each independently represent a linear or branched alkyl group having at most 20 carbon atoms, optionally substituted with any of an aryl group, an alkenyl group, an alkoxy group, a hydroxyl group, a sulfo group, a carboxyl group and an acyloxy group; Ar3 and Ar4 each independently represent a hydrogen atom, an alkyl group having from 1 to 4 carbon atoms, or an aryl group having from 6 to 10 carbon atoms, the alkyl group and the aryl group for these may be optionally substituted with any of an alkyl group, an aryl group and a halogen atom, and Ar3 and Ar4 may be bonded to each other; Y4 and Y5 may be the same or different, each representing a sulfur atom, an oxygen atom, a selenium atom, a dialkylmethylene group having at most 12 carbon atoms, or xe2x80x94CHxe2x95x90CHxe2x80x94; Z3 to Z10 may be the same or different, each representing a hydrogen atom, a hydrocarbon group, an oxy group, an electron-withdrawing group or a heavy atom-containing substituent, and at least one of these is an electron-withdrawing group or a heavy atom-containing substituent; two neighboring groups of Z3 to Z10 may be bonded to each other to form a 5- or 6-membered ring; Xxe2x88x92 represents an ion of CF3SO3xe2x88x92.
The recording material of the present invention is for xe2x80x9cheat-mode exposurexe2x80x9d, and this means that the recording material is subjected to heat-mode exposure for image formation. The specifics of heat-mode exposure are described in detail below. As in Hans-Joachim Timpe, IS and Ts NIP 15:1999 International Conference on Digital Printing Technologies, page 209, it is known that, with regard to a process comprising photo-excitation of a light-absorbing substance (e.g., dye) in a photographic material followed by chemical or physical change thereof for image formation in a layer of the material, the process of image formation comprising photo-excitation of the light-absorbing substance followed by chemical or physical change thereof includes two major modes. Specifically, one is a photon mode in which the photo-excited light-absorbing substance in the photographic material is inactivated through photo-chemical interaction (for example, energy transfer or electron transfer) with another reactive substance in the material, and the reactive substance having been thus activated as a result of the interaction undergoes a chemical or physical change necessary for image formation in the layer of the material; and the other is a heat mode in which the photo-excited light-absorbing substance in the photographic material generates heat and is thus inactivated through the heat generation, and the other reactive substance in the material receives the heat and undergoes a chemical or physical change necessary for image formation in a layer of the material. Other minor modes of the process are omitted herein; for example, ablation, in which the substances in a photographic material are explosively scattered by some locally focused light energy, and multiphoton absorption, in which one molecule in a photographic material absorbs a number of photons all at one time.
The modes of the exposure process are referred to as photon-mode exposure and heat-mode exposure. The technical difference between photon-mode exposure and heat-mode exposure is whether or not energy quantities from a plurality of photons for exposure can be added up for the intended reaction. For example, referred to is a reaction through exposure to a number, n, of photons. In the photon-mode exposure, which takes advantage of photo-chemical interaction of the substances in a photographic material, the energy quantities from the n photons cannot be added up for the reaction because of laws of quantum energy and momentum conservation. In other words, every reaction through photon-mode exposure requires the condition xe2x80x9cquantity of energy of one photonxe2x89xa7quantity of energy for one reactionxe2x80x9d. On the other hand, in the heat-mode exposure, the light-absorbing substance in the photographic material is first photo-excited to generate heat, and the heat thus having been converted from light energy serves for the reaction for image formation in a layer of the material. Accordingly, in the heat-mode exposure, the energy quantities of all n photons can be added up for image formation. Therefore, the condition of xe2x80x9cenergy quantity of n photonsxe2x89xa7energy quantity for one reactionxe2x80x9d will be sufficient for the heat-mode exposure. However, the addition of the energy quantities in the heat-mode exposure is restricted by heat diffusion. Specifically, if an exposed area (reaction point) of a photographic material successively undergoes a subsequent photo-excitation and inactivation before heat generated therein by a previous photo-excitation and inactivation step goes out through heat diffusion, and therefore successively receives heat through successive photo-excitations and inactivations, then the heat quantities can be surely accumulated and added up to elevate the temperature of that exposed area. However, if the heat generation in the subsequent step is too late, the heat generated in the previous step will go out of the area through heat diffusion. In other words, in heat-mode exposure to a predetermined level of total energy, a case of short-time exposure to higher energy and a case of long-time exposure to lower energy produce different results, and the former case of short-time exposure to higher energy is more advantageous than the latter case.
Needless-to-say, the photon-mode exposure may also undergo the same phenomenon as above, being influenced by subsequent reaction diffusions, but is basically free from this phenomenon.
The difference between the photon-mode exposure and the heat-mode exposure will be discussed with respect to the characteristics of a photographic material to be processed. In the photon-mode exposure, intrinsic sensitivity (the quantity of energy necessary for the reaction for image formation) of a photographic material is always constant relative to the exposure power density (W/cm2) (=energy density per unit exposure time); but in the heat-mode exposure, the intrinsic sensitivity increases with an increase in the exposure power density. Now, the exposure time is fixed to suffice for practicable image-recording materials, and the two modes are compared for the thus-fixed exposure time. In photon-mode exposure, in general, a low degree of energy of about 0.1 mJ/cm2 or so may be enough for high-sensitivity exposure of the materials, but even a slight amount of exposure will cause photo-reaction in the materials. Therefore, in this mode, the materials often involve a problem of low-exposure fogging in a non-exposed area. On the other hand, in heat-mode exposure, the photographic materials do not undergo photo-reaction if the amount of exposure is not above a certain level. In this mode, in general, the photographic materials require a level of exposure energy of 50 mJ/cm2 or so, in view of their thermal stability, and are therefore free from the problem of low-exposure fogging in the non-exposed area.
In fact, in heat-mode exposure, photographic materials require an exposure power density of at least 5000 W/cm2 on their surface, preferably at least 10000 W/cm2. Though not described in detail herein, high-power density lasers of higher than 5.0xc3x97105 W/cm2 are undesirable, as they cause ablation and soil light sources and other units.